The invention relates to improvements in methods of and in apparatus for manipulating sheet-like products, and more particularly to improvements in methods of and in apparatus for winding successive products of a series of non-overlapping or partially overlapping sheet-like products on a rotary core.
It is well known to store streams of partially overlapping or non-overlapping discrete paper sheets or sets of paper sheets on a rotary core so that the sheets are converted into a roll having a plurality of convolutions the innermost of which directly surrounds the core and the outermost of which is exposed. Such procedure is often resorted to for temporary storage of brochures or newspaper sections, for example, for temporary storage of sections which are to appear in the Sunday or weekend editions of daily newspapers. Apparatus which are utilized to wind flexible sheet-like products onto rotary cores further comprise flexible bands which cooperate with the cores in order to ensure that the products remain convoluted on their core or on previously convoluted products for a desired interval of time. To this end, each core is connected or connectable with one end of a single band or with one end of each of two or more bands in such a way that the band or bands are wound onto the rotating core and form convolutions which alternate with the convolutions of the growing roll. The outermost convolution of the single band or the outermost convolutions of two or more bands surround the outermost convolution of the fully grown roll.
It is often necessary to store sheet-like products wherein one marginal portion is thicker than the other marginal portions. Typical examples of such products are so-called square folded paper sheets wherein at least one of the four marginal portions is or can be much thicker than the marginal portion which is parallel thereto. The same holds true for signatures. Therefore, when a roll consists of square folded sheet-like products, or other products wherein one marginal portion is thicker than the marginal portion which is parallel thereto, the roll of convoluted products is not a true cylinder but rather a truncated cone having a larger-diameter first end face which is formed by the thicker marginal portions and a smaller-diameter second end face which is formed by the (thinner) marginal portions extending in parallelism with the thicker marginal portions. It is assumed here that the winding operation involves advancing the sheet-like products in such a way that the thicker marginal portions are delivered in a direction at right angles to the axis of rotation of the core.
Published German patent application No. 2 207 556 of Gsegnet discloses a winding apparatus which employs a single flexible band having a width greater than the width of the stream of products which are to be convoluted onto a roll. Thus, if the apparatus is to be used to form rolls of square folded sheet-like products, the roll will invariably constitute a conical frustum because the wind band which is employed by Gsegnet is not designed to subject select portions of the growing roll or of the fully grown roll to different compressive stresses. Frustoconical rolls create problems during winding, in storage, during transport, as well as during unwinding. For example, the band or bands are likely to run askew. The situation is aggravated when the winding apparatus is used in a publishing house or in another establishment wherein the characteristics of products which necessitate temporary storage in the form of rolls often vary within a wide range, i.e., the difference between the thicker and thinner marginal portions is not always the same so that the conicity of the rolls varies in dependency upon changes of such differences. The ratio of thicknesses of the thicker marginal portion and of the marginal portion which is parallel thereto can vary in dependency on the number of sheets in a square folded or analogous product and/or in dependency on the quality of the material of the sheets. Therefore, the formation of frustoconical rolls in the apparatus of Gsegnet could not be avoided even by a most careful selection of the elasticity, stretchability and certain other important parameters of the flexible band or bands because it would be necessary to employ a different band for each of a wide variety of different products. The utilization of bands exhibiting certain specific properties (such as a selected resistance to tensional stresses and/or others) would contribute significantly to the cost of the apparatus and would render such cost prohibitive for many potential uses.
Published German patent application No. 33 15 496 proposes to employ a single relatively narrow band which is to be convoluted around the rotating core and around the adjacent convolutions of sheet-like products in zig-zag formation or in the form of a sine curve extending to both sides of the central symmetry plane of the roll (the symmetry plane extends at right angles to the rotational axis of the core and is located midway between the two end faces of the roll). Reference may also be had to commonly owned U.S. Pat. No. 4,538,397 to Boss. Such mode of winding the band also fails to prevent the development of a frustoconical roll if the sheet-like products are square folded sheets or signatures.
Published German patent application No. 25 44 135 of Achelpohl et al. proposes to use two spaced-apart parallel narrow flexible bands to ensure reliable winding of sheet-like products which are supplied in the form of an imbricated stream. The arrangement is such that the convolutions of one band are located at a given distance from one end face of the roll, and the convolutions of the other band are located at the same distance from the other end face of the roll. Achelpohl et al. do not propose to alter the tensional stress upon the one and/or the other band; therefore their apparatus cannot prevent the formation of frustoconical rolls if the components of the imbricated stream are square folded sheets or other products wherein the thickness of at least one marginal portion exceeds the thickness of the other marginal portion or portions.
Published European patent application No. 0 316 563 of Merkli discloses an apparatus which also employs two narrow flexible bands disposed at the same distance from the adjacent end faces of the roll. Therefore, the apparatus of Merkli will turn out acceptable cylindrical rolls as long as the thickness of each sheet-like product is uniform throughout.
In the absence of an acceptable solution, the makers of winding apparatus have accepted that presently known apparatus cannot prevent the making of frustoconical rolls if the constituents of the rolls are square folded sheets, signatures and like products with thicker and thinner marginal portions. As a rule, presently utilized winding apparatus operate with a single relatively narrow band which is located midway between the end faces of the roll. Reference may be had to published European patent application No. 0 135 080 of Merkli. The single band is likely to form a constriction midway between the end faces of the roll so that the convoluted sheets form a substantially hourglass-shaped body which is acceptable in most instances as long as the diameters of the two end faces are at least substantially identical. Such configurations can be achieved if the thickness of each and every portion of each sheet-like product in the roll is the same.
If the difference between a relatively thick marginal portion and the marginal portion which is parallel thereto is very pronounced, one end face of the resulting frustoconical roll is likely to reach the maximum permissible diameter (e.g., for the purposes of storage or further manipulation) well before the roll contains that number of products which could be stored if the thickness of each product were the same throughout. This entails less than optimum utilization of conventional apparatus and increased space requirements for storage of a particular number of sheet-like products.